Is tough mudder really that hard? Might work in certain areas (seems a lot of finance bros are pretty in to it) but as far as actually finishing one, it seems like a lot of not very athletic people don't have trouble making it across the line. Would definitely not put it down if its something you just did once...or even if you have done your local one a few times. Unless you have traveled to be able to do it more than once per year, its probably not a good resume thing. The thing that almost always came up in interviews that was on my one line of interests was Cyclocross. It is far more specific than "I Like Bikes" and is something different that a lot of people were curious about. Sailing came up as well, but that was more because it was in the body of my resume since I was the captain of the college team. Things like Tennis are just throwaway answers for most resumes since it just equates with "Oh no way man, you own a tennis racket too?". Basically, if you have something on that line that sounds interesting, it can help give you something to talk about in the interview. Something that helps you pass the test of "do I like interacting with this person".